1. Field of the Invention
The present invention relates to a substrate for manufacturing a semiconductor device with an SOI (silicon on insulator) structure and to a manufacturing method thereof.
In this specification, a semiconductor device means a device in general which can operate utilizing semiconductor characteristics. An electrooptic device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
With development in VLSI technology, demanded levels of integration, operation speed, and power consumption have been higher. In order to satisfy these requirements, an SOI structure is receiving attention. In this technology, an active region (channel formation region) of a field-effect transistor (FET), which is conventionally formed with bulk single-crystalline silicon, is formed with a single-crystalline silicon thin film. It is known that use of the SOI structure enables manufacturing a MOS field-effect transistor with smaller parasitic capacitance than in the conventional case of using a bulk single-crystalline silicon substrate, and is advantageous to high speed operation.
As an SOI substrate, a SIMOX substrate or a bonded substrate is known. An SIMOX substrate is formed in the following manner: oxygen ions are implanted into a single-crystalline silicon substrate and heat treatment is performed at 1300° C. or higher to form a buried oxide layer, so that a single-crystalline silicon film is formed on the surface and thus an SOI structure is obtained. In the SIMOX substrate, oxygen ion implantation can be controlled precisely and thus a single-crystalline silicon film can be formed with an even thickness; however, oxygen ion implantation takes much time and there are problems in time and costs. Further, there is another problem in that a single-crystalline silicon substrate is damaged easily in the oxygen ion implantation, so that an obtained single-crystalline silicon film can be influenced.
A bonded substrate is formed in the following manner: two single-crystalline silicon substrates are bonded to each other with an insulating film interposed therebetween and one of the single-crystalline silicon substrates is thinned, so that a single-crystalline silicon film is formed to obtain an SOI structure. As a method for thinning a film, a hydrogen ion implanting separation method is known. In the hydrogen ion implanting separation method, hydrogen ions are implanted into one single-crystalline silicon substrate to form a microbubble layer at a given depth from a surface of the silicon substrate; the microbubble layer functioning as a cleavage plane, a single-crystalline film can be fixed to the other single-crystalline silicon substrate (see Reference 1: Japanese Published Patent Application No. 2000-124092).
In recent years, an attempt to form a single-crystalline silicon film over a substrate having an insulating surface, such as glass, has been made. As an example of an SOI substrate in which a single-crystalline silicon film is formed over a glass substrate, one devised by the present applicant is known (see Reference 2: Japanese Published Patent Application No. H11-163363).